Maize Downy Mildew and Effects of Varieties and Metalaxyl Identification of Maize Downy Mildew Pathogen in Lampung and the Effects of Varieties and Metalaxyl on Disease Incidence Cipta Ginting1*, Joko Prasetyo1, Suskandini Ratih Dirmawati1, Ivayani1, Paul Benyamin Timotiwu2, Tri Maryono1, Widyastuti3, Damar Indah Ryska Chafisa4, Alim Asyifa4, Erisa Setyowati4, and Ambos Harry Zuisent Pasaribu4 1Departement of Plant Protection, Faculty of Agriculture, University of Lampung, St. Soemantri Brojonegoro No.1 Bandar Lampung City, Lampung, Indonesia 2Departement of Agronomy, Faculty of Agriculture, University of Lampung, St. Soemantri Brojonegoro No.1 Bandar Lampung City, Lampung, Indonesia 3Integrated Laboratory and Technology Innovation Center at University of Lampung, St. Soemantri Brojonegoro No.1 Bandar Lampung City, Lampung, Indonesia 4Departement of Agrotechnology, Faculty of Agriculture, University of Lampung, St. Soemantri Brojonegoro No.1 Bandar Lampung City, Lampung, Indonesia *[email protected] (Cipta Ginting), +62 82281286464 [email protected] (Joko Prasetyo), +62 85269328546 [email protected] (Suskandini Ratih Dirmawati), +62 85624512267 [email protected] (Ivayani), +62 81373525491 [email protected] (Paul Benyamin Timotiwu) +62 81315763841 [email protected] (Tri Maryono), +62 81540951446 [email protected] (Widyastuti), +62 85268250114 [email protected] (Damar Indah Ryska Chafisa) [email protected] (Alim Asyifa) [email protected] (Erisa Setyowati) [email protected] (Ambos Harry Zuisent Pasaribu) *Corresponding outhor List of Tables/Figures: Table 1 Morphology and morphometry (µm) of conidiophores and conidia of Peronosclerospora from diseased maize plants Table 2 Spesies of Peronosclerospora identified from specimen of diseased maize plants in the Province of Lampung Table 3 Disease severity, AUDPC, infection rate (r), and production of maize F1 and F2 of NK- 22 and P-27 Table 4 The number of stomata and their size formed by NK-22 dan P-27 F1 dan F2 maize Table 5 Disease severity, AUDPC and infection rate (r) of downy mildew of F1 and F2 NK-22 maize variety treated with metalaxyl at three concentration levels Table 6 Disease severity, AUDPC and infection rate (r) of downy mildew of F1 and F2 P-27 maize variety treated with metalaxyl at three concentration levels Figure 1. Conidia and conidiophores of Peronosclerospora: P. sorghi (a, b, c), P. maydis (d, e, f), and P. philippinensis (g, h, i) observed under light microscope (a, d, g) or scanning electrom microscope (b, c, e, f, h, i). Arrows in (a) and (d) show type of branching and arrows in (g) show cylindrical conidia. Conidiophores emerge singly (c) or in group (f, i) from stomata Figure 2. Oospores of Peronosclerospora: P. sorghi (a) and P. philippinensis (b) Figure 3. Graphics of AUDPC from 7 to 35 days after inoculation: variety of NK-22 F1 and F2 (a); variety of P-27 F1 and F2 (b); F1 of P-27 treated with 0, 2, and 4 g metalaxyl (c); F2 of P- 27 treated with 0, 2, and 4 g metalaxyl (d); F1 of NK-22 treated with 0, 2, and 4 g metalaxyl (e); F2 of NK-22 treated with 0, 2, and 4 g metalaxyl (f) Identification of Maize Downy Mildew Pathogen in Lampung and the Effects of Varieties and Metalaxyl on Disease Incidence ABSTRACT Maize downy mildew (MDM) is concidered as a major problem in all maize growing areas in Indonesia including the Province of Lampung. The objectives of this study were (i) to identify the species of Peronosclerospora causing maize downy mildew (MDM) in Lampung, (ii) to determine the influence of varieties on the intensity of downy mildew and (iii) to determine the efficacy of metalaxyl to control MDM on some maize varieties. To identify Peronosclerospora causing MDM, the pathogens were observed under light microscope and scanning electrom microscope. Maize varieties response against pathogens and efficacy metalaxyl were researched in the field with the test plants exposed to plants showing MDM symptoms as the sources of inocula to mimic natural conditions. Three species of Peronosclerospora were found, i.e. P. sorghi, P. maydis, and P. philippinensis. P. sorghi, P. maydis, and P. philippinensis. However, the presence of the Peronosclerospora species reported here is tentative pending further studies with molecular techniques. On both varieties Pioneer 27 (P-27) and NK-22, AUDPC on F1 plants was greater than that on F2 plants. On P- 27, the production of F2 was higher that that of F1 plants, but there is no significant difference in production between F1 and F2 of NK-22 variety. Seed treatment using metalaxyl was not effective to control downy mildew of maize. Keywords: maize downy mildew, metalaxyl, mildew, Peronosclerospora sorghi, P. maydis, P. philippinensis INTRODUCTION Downy mildews have been reported to cause crop diseases in many countries (Crandall et al., 2018; Rashid et al., 2013). Maize downy mildew (MDM) is a serious disease affecting maize production in many parts of Indonesia, including the Province of Lampung (Muis et al., 2016; Widiantini et al., 2015; Hikmahwati et al., 2011; Semangun, 2004). Infected maize plants show two types of symptoms, i.e. systemic symptom and local symptom. The systemic symptom occurs when the invading pathogen has reached its growing point (that is located at the top of the stalk tissue of the plant). In infected young plants, newly formed leaves show symptoms of small chlorotic spots. These patches develop into parallel with the leaf bone. The affected plants become dwarf. If the pathogen does not reach the growing point, local symptoms will occur in the form of chlorotic lines on the leaves. In the morning, there is a layer of white velvet, consisting of conidia and conidiophores of the fungus, on the underside of the affected leaf (Semangun, 2004). MDM in Indonesia is caused by three Peronosclerospora species, i.e. P. maydis, P. sorghi, and P. philippinensis (Hikmahwati et al., 2011; Muis et al., 2016). Previously, P. maydis was reported to be restricted to Indonesia and Australia, while P. sorghi distributed worldwide including America, Asia, Africa, Europe and Australia. Janruang & Unartngan (2018) reported that P. maydis was found in several locations in Thailand. P. philippinensis is widely distributed in Asia (International Maize and Wheat Improvement Center [CIMMYT], 2012). In Lampung, the causal agent of MDM was reported to be P. sorghi (Muis et al., 2016) and P. maydis (Muis et al., 2013; Semangun, 2014). In Central Lampung, the causal agent of MDM was reported to be P. sorghi (Muis et al., 2016), P. maydis (Muis et al., 2013). It was probably both spesies of Peronosclerospora existed in Central Lampung. More extensive survey should be conducted to determine what spesies of Peronosclerospora causing MDM in Lampung. MDM is often controlled by planting resistant varieties and/or preplanting seed treatment using the synthetic fungicide metalaxyl (Semangun, 2004). The use of fungicide metalaxyl has caused the emergence of resistant Peronosclerospora population (Widiantini et al., 2015; Surtikanti, 2013; Isakeit & Jaster, 2005). The occurrence of metalaxyl resistance was also reported in other pathogens. For example, out of 116 isolates of Phytophthora infestans causing potato late blight tested for metalaxyl resistance, 25.9% were found to be resistant, 19.8% was intermediate and 54.3% was sensitive to metalaxyl (Aav et al., 2015). Thus, maize plants are often damaged due to MDM although hybrid improved maize seeds are planted. In addition, farmers often use F2 seeds that are harvested from original F1 hybrid seed that may be considered expensive. Thus, it should be ascertained whether the response of various varieties and their progenies (F1 and F2) are different against pathogens that exist in the field. In addition, it is necessary to assess whether a specific variety or the progenies showed different responses to metalaxyl. The objectives of this study were to identify the species of Peronosclerospora causing MDM in the Province of Lampung, to determine the influence of maize variety and its progeny on the intensity of MDM, and to determine the efficacy of metalaxyl to control MDM on some maize varieties. METHODS The first part of this research was identification of the pathogen causing MDM in all major maize production areas in the Province of Lampung. In addition, three experiments were conducted from April 2016 to May 2017. They were (1) the effect of maize variety and its progeny on MDM, (2) the efficacy of metalaxyl on NK-22 F1 and F2, (3) the efficacy of metalaxyl on P-27 F1 and F2. Identification of Peronosclerospora Species Causing MDM in Lampung First, maize plants in vegetative phase showing systemic or non-systematic symptoms were observed in eight regencies or city in Lampung, namely Central Lampung, South Lampung, East Lampung, North Lampung, West Tulang Bawang, Bandar Lampung, Pasawaran, and Pringsewu. Efforth was made to take plant samples from two fields from each regency/city and to take two plants from each field. Plant samples were uprooted with the soil around the base of the stem and then was placed into polybags individually. Each plant was covered with transparent plastic bag to reduce stress during transportation to the laboratory and to avoid the pathogen spread among the sample plants. During the identification process in the laboratory, the plants were placed individually in a 1-m high plastic enclosure also to prevent pathogens from spreading among the sample plants. Pathogen sporulation – in which timing is crucial - was stimulated by modified procedure from Rustiani et al. (2015). A maize plant in a polybag was transferred to the laboratory. In the afternoon in the laboratory, the third leaf from the shoot with the symptoms was washed by rubbing the leaves with two fingers while rinsed with running water and then dried with tissue paper. The washing was aimed to keep moisture and ensure clean stomata from dirts and fungus propagules.